The following quinolone-carboxylic acid of the formula: ##STR2## is known in the art as having potent antibacterial activities. This compound, 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-quinoline-3-car boxylic acid, generally called "Ciprofloxacin" (hereinafter, referred to as "Ciprofloxacin") has been widely used for the treatment of infectious diseases in mammal caused by bacteria. See, P. B. Fernandes ed., International Symposium on Quinolones, pp. 1-134, J. R. Porous, S. A., Barcelona, Spain (1989).
Although Ciprofloxacin is very active in treating bacterial disease, the compound has certain disadvantages in that it is almost insoluble or sparingly soluble in water. This property bars the compound from formulating it into injectable solutions.
Aiming at overcoming these disadvantages, various acid and base addition salts of Ciprofloxacin have been developed, which can easily dissolve in water to a desired extent and do not cause occurrence of precipitation in the resulting solution during storage. For example, U.S. Pat. No. 4,705,789 to Grohe et al. discloses that hydrochloride, methanesulfonate, acetate, propionate, succinate and lactate of Ciprofloxacin are suitable to prepare highly stable injectables. These salts, however, cause some problems from the pharmaceutical point of view. That is, Ciprofloxacin hydrochloride is unstable in solution; methanesulfonate exhibits a very low value of pH; and acetate and propionate smell unpleasant. Ciprofloxacin lactate tends to occur precipitation in an injection when it is contained in the injection in an excessive amount.
European Patent Publication No. 0 067 666 A1 suggests to use galacturonic acid, aspartic acid, glutamic acid and gluconic acid as an acid for forming salts with Norfloxacin or Enoxacin which do not cause such precipitation in solution. The salts formed by adding these acids are proven to be pharmaceutically valuable.
German Patent Application Nos. P35 00 243.3 and P35 17 709.8 disclose sodium hydroxide, potassium hydroxide, ethanolamine, lysine, N-methyl glucamine and arginine as the bases which can form non-precipitating salts with Ciprofloxacin. However, an aqueous solution of each salt derived from those bases is not suitable to be administered parenterally owing to its high pH value.